[argyllcms] Re: Feature request (and an implied question)

  • From: Matthieu DUBAIL <matthieu.dubail@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Tue, 27 Jul 2010 02:16:11 +0200

Hi Ben,

I'm pretty sure that the problem with EV or Guide Number calculation here
(apart from proper calibration constant) is that you need to know the
distance of the light source.
It might be risky to do measurement at 1m if you're light source is too low
(too much spectro sensor noise).
It's sometime impossible if your light source is too high (spectro sensor

Matthieu DUBAIL

2010/7/26 Ben Goren <ben@xxxxxxxxxxxxxxxx>

> > One issue to consider is that readings from different light meters are
> only comparable if they have the same directional characteristics. I think
> the i1 has a light measurement head with a cosine response, while many light
> meters intended for photographic purpuses have different directional
> characteristics (e.g. hemispherical), see also
> http://en.wikipedia.org/wiki/Light_meter
> Thanks for the caution. This particular meter has a retractible dome; in
> the retracted position, it&rsquo;s supposed to be a ``flat field'' response
> that, by eyeballing it, would be the same basic geometry as the i1 (though
> the aperture sizes differ, of course).
> b&

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